Decolorizing process



Patented Oct. 10, 1933 UNITED 3 STATES PATENT. orrlcs mass: nsconomzmc raocsss' Marvin J. Reid, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New York No Drawing. Application June 14, 19::- Serial No. 611.251

scum. (01. 252-1) This invention relates to a process of decolorizing cellulose ester materials, and more particularly to a process for decolorizing dyed cellulose acetate sheets or films.

A variety of cellulose ester plastic products,

especially photographic films, thin sheeting used for wrapping-purposes and the like, are coloredcountered in such recovery processes is the removal of dyestuffs and other coloring matter.

Although colored films and sheetings may be bleached by various solvents and solvent combinations, and the dye eventually removed, such processes are sometimes ineffective to completely decolorize the material and, unless the material is reduced to an extremely fine state of subdivision, are generally exceedingly time-consuming and inconvenient. In the case of nitrocellulose film scrap, thereis considerable danger in grinding the material sumciently 'fine for penetration of the bleaching solvents due to the inflammable character of nitrocellulose.

The present invention has forits principal object to provide a simple and efiective method of decolorizing cellulose ester scrap materials, such as those produced from dyed photographic film and thin sheeting. A further object is to provide a method in which the decolorizing or bleaching agent may act upon the material with a consumption of time. Another ob- "ject is to provide a method whereby cellulosic films produced from such materials as cellulose nitrate, cellulose acetate, or other cellulose organic esters, or cellulose ethers, may be decolorizedwithout preliminary subdividing and grinding operations. A specific object is to provide amethod for decolorizing a dyed cellulose acetate sheeting scrap with the customary bleaching agents. Other objects will hereinafter appear.

These objects are accomplished by, the following invention which, in its broadest aspects,

' comprises a combination of the following steps.

The colored scrap material is first dissolved in a suitable solvent to produce a colored solution or dope. This is mixed with a suitable sheeting andallied products. In the interestof econv precipitant,'such as water, or other non-solvent, the cellulosic material being thereby precipitated in a light, porous form still having most of .the dye incorporated therewith. The precipitated material is filtered off, bleached by mixing with a suitable bleaching agent such as chlorine water and thereafter leached counter-currently with methyl alcohol which removes the soluble chlorides produced in the bleaching operation. The decolorizedlmaterial is washed, dried, and is then in a, condition immediately available for re-use in the manufacture of films, cellulosic In the following. example, I have set forth one f of the preferred embodiments of my invention, 'l0

but it is included merely-for purpow of illustration and not as a limitation thereof; I

- Example a 10 grams of colored cellulose acetate thin '75 sheeting scrap material is dissolved in grams of acetone to produce acolored dope; The dope is then run into an' excess of hot water contained in a suitable receptacle and maintainedj at a temperature of 120 F. The soft, porous so cellulose acetate is immediately precipitated still containing the dye-stuff. "After precipitation "is completed, the material is filtered from the solution and bleached with saturated chlorine water for one hour at room temperature, which 85 converts the dyestufls to colorless compounds and occasions the formation of soluble chlorides. It is then separated from the bleaching solution and leached .by three one-hour counter- 'curren t changes of methyl alcohol at a temperature of 80 F. to remove the soluble chlorides formed during the chlorine water treatment. The leached precipitate which is light and porous in character is then dried after which it may be re-used in the manufacture of photographic film, thin sheeting and the like.

Although in the above example I have described my process with reference to colored cellulose acetate thin sheeting, it is not in any way limited thereto. The process is equally applicable to the treatment of thin or thick sheets of cellulosic materials, although it is desirable in the case of thicker sheeting to cut the ma-' terial into smaller pieces than is necessary with thinner stock. The invention is. of course, not limited to the treatment of cellulose acetate, but may be applied to the decolorizing of cellulose nitrate,'cellulose ethers, such as benayl cellulose, and-the higher or mixed cellulose organic butyrate, or cellulose acetate prop'ionate, cellulose acetate butyrate, and the like.

The cellulosic material will in the first instance be dissolved in any appropriate solvent. Solvents for cellulose acetate, for example,

include acetone, methylene chloride, methyl ace-.

tone, methyl acetate, ethyl acetate, 1-4 dioxane, ethyl lactate, diacetone alcohol, and others. Likewise, the precipitant may be selected from a wide range of suitable substances, typicalof ethers as precipitants. The solvents and precipitants of themselves form no part of the present invention, since they are for the most part well known to those skilledin the art, both solvents and precipitants, of course, being selected upon the basis of suitability for use with the particular cellulosic compound dealt with.

Although I.have found chlorine water to be a,particularly effective bleaching agent for removing the color from the precipitated cellulosic material, I may use with equally satisfactory results sodium and calcium hydrochlorites, chlorine gas, and other known bleaching agents.

My process is particularly distinguished by the fact that cellulose acetate or other cellulosic material are brought into a physical conditionin which the bleaching agent can quickly and effectively penetrate therein and perform its decolorizing function. This makes possible a pronounced saving in the recovery of colored scrap sheeting and photographic film, inasmuch as the material is immediately brought intoa condition in which the dye may be removed directly, thereby eliminating the necessity for the dangerous and inconvenient grinding operations of the prior art. So far as I am aware, no process thus far known to the art involves a method whereby the cellulosic material is brought into apporous, precipitated condition prior to the bleaching treatment. 1

. In the above specification and appended claims, reference to cellulosic scrap material is intended to include scrap produced fromeither photographic film or. from thin sheeting, such as that used for wrapping purposes, or any other cellulosic scrap material.

As many apparently widely diiferentembodiments of this invention may be made without de parting from the spirit thereof, it is to be understood that I do not limit myself to the foregoing example or description except as indicated in the following patent claims. 1

What I claim' as my invention and desire to be secured by Letters Patent of the United States is:

1. The process of decolorizing a dyed cellulosic scrap material which comprises dissolving the material in a solvent therefor, precipitating the material from solution by means of a non-solvent therefor, and thereafter bleaching the dye out of the precipitate while in a relatively open, porous condition.

2. The process of decolorizing a dyed cellulosic scrap material which comprises dissolving the material in a solvent therefor, precipitating the material from 'solutionby meansof water, and thereafter bleaching the dye out of the precipitatewh'ile in a relatively open, porous condition.

3. The process of decolorizing a dyed cellulose ester scrap material which comprises dissolving the'material in a cellulose ester solvent, precipitating the cellulose ester from solution by with a cellulose ester non-solvent therefor, and thereafter treating the precipitate while in a relatively open, porous condition with a bleaching agent.

4. The process of decolorizing a dyed cellulose acetate sheet scrap material which comprises dissolving the material in acetone, passing the resulting solution into an excess of water, and thereafter treating the rived cellulose acetate 115 precipitate while in a relatively open, porous condition with an .aqueous chlorine-containing bleaching agent.

5. The process of decolorizing a dyed cellulose acetate sheet scrap material which. comprises 190 dissolving the material in acetone, passing theresulting solution into an excess of water, and thereafter treating the (Lved cellulose acetate precipitate while in a relatively open. porous condition with chlorine water.

, MARVIN J 

